The present invention relates to organometallic compounds which are used for forming thin film comprising ruthenium, ruthenium oxide, or high-purity platinum on a substrate through metal-organic vapor-phase epitaxy. More particularly, the present invention relates to such organometallic compounds which are useful for producing, for example, electrode material used in semiconductor devices and parts.
Conventionally, in advanced technical fields related for example to electrode materials for semiconductor devices, organic ruthenium compounds and organic platinum compounds have been employed for forming a variety of ruthenium thin films and platinum thin films through metal-organic vapor-phase epitaxy. In order to form a ruthenium thin film, ruthenocene; i.e., an organic ruthenium compound represented by formula 3: 
is employed as a source.
The organic ruthenium compound represented by formula 3 has 5-membered rings containing exclusively carbon atoms and hydrogen atoms. In this compound, a ruthenium atom is sandwiched by two 5-membered rings.
In order to produce a platinum thin film, a compound represented by formula 4: 
has conventionally been employed as a source compound. In this organic platinum compound, one 5-membered ring; i.e., a cyclopentadiene ring, forms a bond with the platinum atom, and three methyl groups serve as ligands or form bonds with the platinum atom.
However, the organic ruthenium compound represented by formula 3 has a melting point of 198xc2x0 C. Moreover, an organic platinum compound represented by formula 4 in which R1 is H has a melting point of 65xc2x0 C., and a similar compound in which R1 is CH3 has a melting point as high as 30xc2x0 C. These compounds have relatively low vapor pressure, and control of vaporization rate thereof is disadvantageously difficult.
Difficulty in controlling vaporization rate induces variation in thin-film-formation rate, and results in production of thin film lacking in accurately controlled thickness and flatness.
In addition, the aforementioned ruthenium compound and platinum compounds may be decomposed during heating for vaporization. Thus, poor thermal stability thereof is pointed out in the actual production field.
In recent years, there has been persistent demand for further size-reduction in electronic apparatus, and the target level of integration and packaging density of semiconductor devices and parts has further increased. Accordingly, ruthenium thin film, ruthenium oxide thin film, and high-purity platinum thin film which are incorporated into semiconductor devices and parts are required to have a further smaller thickness.
In connection with such a technical trend, so long as compounds exhibiting a variable film-formation rate are employed as sources, strict quality control of produced thin film cannot be attained, thereby generating variation in quality among products. This problem becomes grave as the thickness of devices decreases and the target film thickness decreases further. Unless the problem is solved, formation of thin film by using conventional source compounds inevitably faces a limitation and does not satisfy demands in the market.
In view of the foregoing, the present inventor has conducted earnest studies, and have developed organometallic compounds which solve the drawbacks of the conventional organic ruthenium compound represented by formula 3 and organic platinum compounds represented by formula 4.
In general, a process for forming thin film broadly comprises three steps: (1) vaporizing a source so as to permit feeding of the source onto a substrate; (2) feeding the vaporized source onto the substrate; and (3) depositing particles of the fed source on the substrate. In metal-organic vapor-phase epitaxy, a compound source is typically used instead of an elemental source.
The reason for not using an elemental source is that the source itself has a relatively low vapor pressure and is difficult to feed. Therefore, the elemental source is converted to a compound source having a relatively high vapor pressure so as to transport the source. However, when the organic ruthenium compound represented by formula 3 and organic platinum compounds represented by formula 4 are employed as sources, a constant film-formation rate is not obtained, possibly due to a low vapor pressure of the sources.
If the vapor pressure of a source is a sole issue to be considered, increasing the molecular weight of the source would be the easiest solution. However, ruthenium thin film, ruthenium oxide thin film, and high-purity platinum thin film which are employed in the semiconductor industry must have a high level of quality which cannot be attained by such a simple approach. For example, to meet the required quality and properties, several factors must be considered, which include crystalline state, lattice constant, thermal expansion coefficient, control of structural defects, mutual diffusion of impurities and constitutional elements, and selective growth.
The organic ruthenium compounds and organic platinum compounds according to the present invention exhibit sufficiently high vapor pressure during vaporization, and thin film obtained from the compounds satisfies properties and quality required in the semiconductor industry.
Accordingly, in claim 1 of the present invention, there is provided an organic ruthenium compound for forming ruthenium thin film or ruthenium oxide thin film on a substrate through metal-organic vapor-phase epitaxy, represented by structural formula 1: 
wherein at least one of the substituents R1, R2, R3, R4, R5, R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2, and R5xe2x80x2 in the two 5-membered rings comprises an alkyl group selected from CH2CH3, CH2CH2CH3, CH2CH2CH2CH3, C(CH3)3, CH2(C6H5), COCH3, COOCH3, and CH2OCH3;, with the case in which R1, R2, R3, R4, R5, R1xe2x80x2, R2xe2x80x2, R3xe2x80x2, R4xe2x80x2, and R5xe2x80x2 all represent hydrogen atoms being excluded.
The above exclusion is made so as to clarify that the ruthenium compounds of the present invention do not include the conventional organic ruthenium compound represented by formula 3 and other known organic ruthenium compounds. Even though conventionally known organic ruthenium compounds are employed as sources of metal-organic vapor-phase epitaxy, vaporization rate is not as constant as that of the organic ruthenium compounds of the present invention. The ruthenium compounds of the present invention represented by structural formula 1 are more bulky than conventionally known organic ruthenium compounds and have increased thermal stability.
Thus, the organic ruthenium compounds of the present invention are characterized in that at least one of the substituents in the 5-membered cyclopentadiene ring comprises an alkyl group selected from CH2CH3, CH2CH2CH3, CH2CH2CH2CH3, C(CH3)3, CH2(C6H5), COCH3, COOCH3, and CH2OCH3; with the aforementioned case being excluded.
Since in the ruthenium compounds of formula 1 of the present invention, at least one of the substituents of the cyclopentadiene ring has CH2CH3, CH2CH2CH3, CH2CH2CH2CH3, C(CH3)3, CH2(C6H5), COCH3, COOCH3, and CH2OCH3, the molecular weight of the compounds is larger than that of ruthenocene represented by formula 2. As a result, vapor pressure of the vaporized compounds serving as deposition sources increases and a constant vaporization rate is attained as compared with the case of conventional ruthenocene.
In claim 2 of the present invention, there is provided an organic platinum compound for forming platinum thin film on a substrate through metal-organic vapor-phase epitaxy, represented by structural formula 2: 
wherein at least one of the substituents R1, R2, R3, R4, and R5 in 5-membered rings comprises an alkyl group selected from CH3, CH2CH3, CH2CH2CH3, CH2CH2CH2CH3, C(CH3)3, and CH2(C6H5).
In the above compounds, the case in which R1, R2, R3, R4, and R5 all represent CH3 groups and the case in which only R1 is a CH3 group are excluded. The exclusion is made so as to clarify that the platinum compounds of the present invention do not include the conventional organic platinum compounds represented by formula 4 and other known organic platinum compounds. Even though conventionally known organic platinum compounds are employed as sources of metal-organic vapor-phase epitaxy, vaporization rate is not as constant as that of the organic platinum compounds of the present invention.
In the organic platinum compound of the present invention represented by structural formula 2, at least one substituent in the 5-membered cyclopentadiene ring comprises an alkyl group selected from CH3, CH2CH3, CH2CH2CH3, CH2CH2CH2CH3, C(CH3)3, and CH2(C6H5), thereby providing more bulky molecules and elevating the molecular weight of the compounds as compared with conventional organic platinum compounds represented by formula 4. As a result, vapor pressure of the vaporized compounds is higher than conventional organic platinum compounds, bulkiness also increases, and a constant vaporization rate is attained.
Since the organometallic compounds represented by the aforementioned formulas 1 and 2 have a bulky alkyl group attached to a cyclopentadiene ring, other reactive elements encounter difficulty in approaching Ru or Pt. Therefore, decomposition to metallic platinum or platinum oxide is prevented as compared with the case of organic platinum compounds represented by formula 2. Thus, the organometallic compounds as described in claims 1 and 2 exhibit constant vaporization characteristic and thermal stability when they serve as compound sources of metal-organic vapor-phase epitaxy.
In addition, substituents selected in the present invention contain carbon and hydrogen, and optionally oxygen, depending on the substituents, and contain no other constitutional element. Thus, the amounts of impurities in the formed thin film do not increase. Particularly, a formed platinum film shows considerably high purity without losing the aforementioned characteristics so far as research has determined.
Several methods are contemplated for producing organic ruthenium compounds and organic platinum compounds. The methods will next be described by way of examples.